1. Field of the Invention
The present invention relates to power transmission belts of the type having longitudinally extending, load carrying cords and, more particularly, to a method of removing that portion of the load carrying cords directly exposed at the side surfaces of the belts that are otherwise prone to fraying and/or being separated for the belt during operation. The invention is further directed to an apparatus for automatically removing the exposed cords. The present invention is still further directed to a power transmission belt in which otherwise exposed cords are cut out/ground at the side surfaces of the belt to prevent the aforementioned problem of fraying.
2. Background Art
It is known to sequentially build up belt components on a forming drum to define a belt sleeve, to vulcanize the sleeve, and to divide the vulcanized sleeve into a plurality of individual belts. Such a process is commonly used to form synchronous belts, V-ribbed belts, and V-belts. One component of each of these belts is a load carrying cord, which defines the neutral axis for the belt. Typically, the cord is spirally wound over underlying belt components on the drum. Cutting of the individual belts results in exposure of the load carrying cord at the side surfaces of each belt. The extent of exposure depends upon the tightness of the spiral in which the cord is wrapped. In any event, the cord is generally exposed at less than the entire longitudinal extent of the side surfaces of the belt and commonly at 2 or more discrete locations on each side surface of the belt. In those belts in which the side surfaces are not covered by a canvas layer, or the like, the exposed cord repeatedly contacts cooperating pulleys during operation. The frictional forces between the cord and pulley give rise to a raised nap and/or frayed spots. This may result in system vibration during operation.
Another problem with those conventional belts having exposed cords is that the exposed cords are prone to being pulled out of the rubber in which they are embedded. This may not only result in significant, unwanted vibration, but may also compromise the integrity of the belt.
It is known to use polyester fiber for load carrying cords. One proposed solution to the fraying problem associated with polyester fiber cords is disclosed in U.S. Pat. No. 3,200,662. In this patent, it is taught to fuse the frayed cords by heating the cords to a temperature higher than the melting point of the fiber therein.
Aramid fiber has been used to manufacture load carrying cords in power transmission belts due to its good tensile strength, resistance to elongation and good bending characteristics. Aramid fiber load carrying cords have been used increasingly in synchronous transmission toothed belts that are run at high speed and severely bent in operation. The aramid fiber cords are also prone to fraying and/or fluffing upon repeatedly contacting the cooperating pulleys. While the aramid fiber cords have many desirable characteristics that make them suitable for use in power transmission belts, the binding force of the individual fibers defining the cords is relatively weak, making the cord fibers prone to unwrapping. This phenomenon occurs even in belts in which the aramid fiber load carrying cords are embedded and firmly bonded within a rubber layer of the belt. What starts as fraying of the exposed portion of the cords may ultimately result in the individual fibers separating from each other and being pulled out of the belt as the cords repeatedly contact cooperating pulleys. The withdrawn fibers may wrap around the belt, the cooperating pulleys and/or the related machinery. This results in potential damage to the belt and/or the machine as well as resulting in the inducement of vibration to the operating system if not ultimate failure of the system.
Various solutions have been proposed to overcome the fraying and fiber separation problems noted above. Most of these solutions involve the enhancement of the fiber bonding force by treatment of the cords. For example, in Japanese Patent Publication No. 31015/1982, a method is disclosed in which the exposed load carrying cords are solidified with an adhesive.
In Japanese Patent Publication No. 26700/1985, a treatment for aramid fiber cords is disclosed in which the cords are immersed in an aqueous solution of polyvinyl alcohol, vinyl acetate or gum arabic, or a solvent solution of acrylic ester. The cords are dried after such treatment.
Generally, enhancing the binding force by an adhesive treatment causes the bending fatigue resistance of the cords to be diminished. The rigidified fibers generally become unsuitable for use in the load carrying cords of a power transmission belt. For example, since hard resin is used for the belt, the solidification of the exposed cord portions with ciano, urethane or epoxy adhesive can substantially rigidify the cords and the belt. The loss of flexibility is determined by the degree of penetration of the adhesive. Even if the aramid fiber cords are bound firmly with adhesive, after long periods of use, the fibers inside of the belt tend to separate from each other. Fraying occurs internally with only the external fibers, soaked in the adhesive, remaining adhered to the rubber. However, it has been found that even if a final twist coefficient is improved and a bonding treatment performed on the cords, the exposed cords eventually develop a raised nap or frayed portion which not only detracts from the appearance of the belt but may result in the withdrawal of the fibers from the belt.
One proposed solution to the above problem has been to manually take out the exposed cords on the side surfaces of the belt, as with a cutter. There are two significant drawbacks with this approach. First of all, it is very time consuming in that it requires the manual manipulation, inspection and cutting of each belt. This becomes very expensive to the manufacturer. Additionally, the procedure may be inconsistently performed on the belts. Localized damage may be inflicted on the belt at the side surface thereof, which may detract from the belt performance.
A still further known method of overcoming the problems of fraying is to arrange the cords so that there is no exposure thereof at the side surfaces of the belt. For example, in Japanese Patent Provisional Publication No. 17242/1990, a method of manufacture is disclosed in which the ends of the cords are not exposed at the belt side surfaces. The problem with this construction is that the strength of the belt is-diminished by reason of the decrease in the number of cords along the width of the belt.